Generally, an integrated circuit (IC) refers to a set of electronic devices, e.g., transistors formed on a small chip of semiconductor material, typically, silicon. Typically, an interconnect structure incorporated into the IC includes one or more levels of metal lines to connect the electronic devices of the IC to one another and to external connections. An interlayer dielectric is placed between the metal levels of the IC for insulation. Generally, the efficiency of the interconnect structure depends on the resistance of each metal line and the coupling capacitance generated between the metal lines. Typically, to reduce the resistance and increase the IC performance, copper interconnect structures are used.
As the size of the IC decreases, the spacing between the metal lines decreases. This leads to increase in the coupling capacitance between the metal lines. Increase in the coupling capacitance between the metal lines has a negative impact on signal transmission along metal lines. Furthermore, increase in the coupling capacitance increases energy consumption of the integrated circuit.
One conventional technique to reduce the capacitive coupling between adjacent metal lines involves replacing a high k dielectric material that separates the metal lines with a low k dielectric material. Another conventional technique to reduce the capacitive coupling involves forming an air gap between adjacent metal lines. Each of these techniques, however, requires processing that can damage and extrude the metal lines. Additionally, the conventional technique of replacing a high k dielectric material with a low k dielectric material results in poor adhesion of the dielectric material.